Multipoint thermocouple assemblies have been used in the past, for example, to obtain information concerning the temperature occurring at different depths or heights in a utilization environment, such as a cracking tower or other process vessel, or the like. Such multipoint thermocouple assemblies may have a length from a few feet to in excess of one hundred feet and are inserted into such process vessel or, more particularly, into a protective well inserted into the process vessel.
A typical known thermocouple assembly includes several thermocouples, each having its measuring junction at a different location along the length of the assembly, and some means for bundling the thermocouples together and for directing their terminating ends to a common junction box for effecting electrical connections to measuring equipment. Usually the measuring junctions and portions of the leads of the thermocouples are contained in a protective tube well that effects such bundling and isolates the thermocouples from the external ambient environment, which may contain corrosives or other material that may affect the thermocouples, for example. Ideally the measuring junctions are held in thermal energy transfer contact with the inside wall of such a protective tube well, so that the thermocouple measuring junctions essentially sense the temperature directly outside of the wall portion of the protective tube well with which they are in contact.
One method of obtaining the desired direct contact of the measuring junctions with the inside wall of the well has been to weld or otherwise fixedly secure the measuring junctions to the inside wall of the well at each location where temperature is to be measured. In addition to the obvious difficulty and special skill and equipment required to effect this method of attachment, undesirable weld effects may result in distorted or specious temperature readings. Moreover, removal of the thermocouples for examination, testing and/or replacement is at best a difficult and time consuming task.
Also known are devices which utilize springs or force exerting components to hold the measuring junctions of the thermocouples against the inside wall of the well. Some devices, for example, employ leaf springs which keep the measuring junctions in an extended condition at all times. Such arrangement however complicates installation of the device into a well, and increases the possibility of damage to the measuring junction during insertion or withdrawal of the device from the well. The springs also are subject to fatigue under prolonged high temperature use which may result in a loss of forcible contact and consequential inaccurate temperature measurement.
Other devices utilizing force exerting components have employed temperature sensitive actuators such as bimetallic springs to effect the desired direct contact. These devices however are relatively expensive and difficult to fabricate. In addition, the contact pressure cannot be controlled very precisely, and may not be adequate if the bimetallic springs are not sufficiently heated. Also, undesirable pressure contact may still be present if the well is heated during insertion and removal of the device.
Another area of concern in the subject art is the inherent difficulty of fabricating and handling multipoint thermocouple devices which, as indicated, may be of substantial length in excess of one hundred feet, for example. Heretofore, flexible devices have been employed which have the advantage that they may be coiled for ease of shipping and installation. Such known flexible devices however typically employ the aforementioned spring actuators and accordingly are subject to the disadvantages associated therewith.